The invention relates in general to gas detectors and in particular to a new and useful device for the transport of a gas sample into a measuring chamber of a detector for the determination of the share of a component in a gas.
The invention refers particularly to alcohol in respiratory air, wherein a piston-cylinder unit serves as the transport element which transports the sample from a gas source through an inlet into the measuring chamber connected to a sensor by means of a flow-connection. Furthermore, a measuring process for the above is given.
German Patent No. 20 35 982 describes such a device with a piston-cylinder unit having a respiration mouth piece for the gas supply from which a sample to be measured is taken by means of a secondary flow, swirled in the cylinder chamber and fed into an analysis device by means of a scavenging stroke. In this known device it is disadvantageous that during the taking in of the air sample from the supply gas, molecules are adsorbed or even condensed on the cylinder wall and therefore they do not reach the detector during the scavenging stroke. Furthermore, once the scavenging stroke is executed, a part of the sample remains in the cylinder chamber and/or in the supply lines leading to the detector, thus it cannot be analyzed and the measuring result is incorrect with a tendency to showing quantitative detection results which are too low.
Furthermore, using piston-cylinder units as transporting elements have the disadvantage that the relatively large friction coefficient between the piston and the cylinder leads to a considerable output loss during operation. This is particularly undesirable when battery-operated devices are employed. The relatively large friction coefficient is mainly determined by the fact that the piston and the cylinder have to be sealed off against each other in the best manner possible in order to prevent leaks or the intake of secondary air.
Another device according to GB-A 2 044 462 has a transport element which leads the sample past the detector during the intake process. Herein it is disadvantageous that not all the molecules have enough time to react with the sensor during the intake process in order to make a contribution to a detection signal. The part of the sample not reacting with the sensor depends on the speed of reaction on the sensitive surface of the sensor in relation to the pumping speed.